Racquets used in ball sports such as tennis, racquet-ball, badminton, and squash generally comprise a head having an oval frame formed on a handle of varying lengths and having strings which extend in perpendicular directions across the head.
The strings are generally strung with a tension in a range between 10 to 70 pounds, depending upon the style of play and preference of the player. The surface of the strings are smooth and slick as manufactured and are generally composed of nylon or animal gut. Over a period of time the smooth strings wear, especially across each other at the intersections of the strings where they are interwoven, creating wear in that location which generally results in the strings breaking.
The accuracy and velocity of the hit ball are two important factors in the play. These factors are often affected by the surface and condition of the strings. Further, another factor in the play is the spin created on the ball when it is hit properly in order to create an altered flight and bounce which is generally harder for the opponent to return. The spin affects the flight and bounce of the ball due to the resistance of the air and the surface of the court such that creating spin results in an advantage over the opponent. The strings must brush over the fuzzy, rough surface of the ball at the moment of hit in order to create the spin, which is relatively difficult since very little friction is developed between the smooth strings of the normal racquet and the surface of the ball.
Heretofore, attempts to increase the roughness of the strings through coating have generally employed an elastomeric material such as natural or synthetic rubber, polyvinyl chloride, alkyd, acrylic, or the like, which may be premixed with a granular substance such as described in the patent to Benson U.S. Pat. No. 3,920,658. Problems have occured in maintaining adhesion in play between the added material and the string of the racquet. Also the abrasive material tends to settle out of the adhesive material when premixed and the added weight of the heavy mixture upsets the delicate balance of the racquet.
Other attempts to prevent wear at the intersections of the strings on a racquet are described in U.S. Pat. No. 3,921,979 which utilizes a self-lubricating plastic cross piece guide which must be placed between each of the racquet strings. This type of construction, although helping prevent wear between the strings, has a tendency to add weight and interfere with the play on the ball.